Cable power?

Discussion in 'General Electronics Chat' started by GARYN, May 21, 2010.

  1. GARYN

    Thread Starter Member

    Sep 4, 2009
    Can anyone explain why the current rating for cable is irrespective of of the voltage, because for example if you choose a relay it will say 10A for 240V i.e 2400w, or 5A at 415V (still the same power-2400w), so why is the cable any differant?
    I have ordered cable for years but never thought about it, it was only today when ordering cable for 110v transformer outlets that i thought
    i could downsize the cable beause its only 110v and not 240v.

    Surly 10A at 500v will put more stress on the cable than 10A at 100v?

    Am i missing something here, thanks in advance.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    The cable is simply a conduit for the electrons. A relay has contacts that will briefly (hopefully) arc when opening and closing. That arcing causes damage to the contact surfaces, and will lead to failure over time. If they get hot, resistance goes up, and so does the rate at which damage accumulates.

    If the insulation is not overstressed, a cable finds amperage to be the same no matter the voltage at either end. As long as the conductor temperature stays below specs, the cable is happy.

    Yes, but only the insulation is affected.
  3. GARYN

    Thread Starter Member

    Sep 4, 2009
    Thanks, that makes perfect sense.
  4. boatsman

    AAC Fanatic!

    Jan 17, 2008
    Firstly cable generally has specifications printed on it e.g. 3 x 1.5 mm 750 volt or 3 x 2.5 mm 750 volt. If you have a coil of 3 x 2.5 mm cable and you use it as an extension cable for a welder if you open up the coil the cable will warm up but if you use the cable as a closed coil the insulation will just burn up with the heat generated. Also bear in mind that if you are using 120 vac for the same amount of power you will need twice the amperage which means much thicker cable.